Once it has been determined where the pipe dips and water has accumulated, mark and clear the surrounding area. The floor will be jack-hammered through so the underground pipe can be accessed. Make sure any major appliances -- such as laundry units or water heaters -- are out of the way.

Utilize professional help to assist with breaking through the floor. With the faulty pipe exposed, consult a professional plumber and reassess the problem. To replace the sagging pipe, remove the old existing pipe.

Properly connect a new PVC pipe in its place with the standard minimum of 1/4" slope per foot toward the street. Make sure all of the pipes are properly sealed and connected.

Backfill the hole and cover it with quick-setting cement. Finish the floor with new tiling.